1. Field of the Invention
The present invention relates to a sheet member holding device for use in a processing apparatus for processing a surface of the sheet member, wherein edges of the sheet member are held in close contact with a peripheral surface of a drum while the drum is axially rotated in a state in which the sheet member is wound around and held on the peripheral surface of the drum.
2. Description of the Related Art
A photosensitive printing plate (hereinafter referred to as a xe2x80x9cprinting platexe2x80x9d) provided with a photosensitive layer formed on a sheet-like support such as a thin aluminum plate is generally used in printing. Printing plates of this type of various sizes having different longitudinal and lateral dimensions are used depending on sizes of printed materials.
In some image exposing apparatuses for performing imagewise exposure onto a printing plate, the printing plate is wound around a rotating drum, and the printing plate is irradiated with light beams according to image data while rotating the printing plate together with the rotating drum to effect scan-expose of the printing plate.
When a printing plate is wound around a rotating drum, opposite edges of the printing plate along a peripheral direction of the rotating drum are nipped and fixed between holding members such as chucks and the rotating drum.
That is, one of the chucks, which corresponds to one of the opposite edges of the printing plate along the peripheral direction of the drum (such as a leading edge in a winding direction) has been previously attached at a predetermined position on the rotating drum, and the other chuck, which corresponds to the other edge of the printing plate (in this case, a trailing edge in the winding direction) is attached at a suitable position depending on the size of the printing plate after the printing plate is wound around the rotating drum.
An exemplary structure of the chuck to be attached to the rotating drum at a suitable position depending on the size of the printing plate is provided with a fixing piece (a supporting post) which can be inserted into any position of an attaching groove formed to extend on the peripheral surface of the rotating drum in the peripheral direction thereof (hereinafter referred to as a xe2x80x9cclampxe2x80x9d). The fixing piece attached to the clamp can be moved to any position along the attaching groove, and can nip the edge of the printing plate at a suitable position corresponding to the size of the printing plate.
By the way, when the printing plate which is wound around the rotating drum is exposed, the printing plate is held in close contact with the peripheral surface of the rotating drum, and is rotated at a high speed together with the rotating drum.
At this time, in order to prevent the edge of the printing plate which is fixed by the chuck portion of the clamp from being lifted partially due to a centrifugal force, a member for promoting a nipping force of the chuck portion nipping the printing plate is provided at a position opposite to the printing plate chuck position with respect to the position of the fixing piece. This member is an urging member such as a spring, and the nipping force of the chuck is increased by an urging force of the urging member.
However, in order to provide an urging force between the holding device such as the clamp described above and the rotating drum, the urging member provide to the holding device need to be brought into contact with the peripheral surface of the rotating drum. This may form unevenness on the peripheral surface of the rotating drum due to scratches and the like.
When a printing plate of a different size is brought into close contact at a position at which the unevenness has been formed, the printing plate does not completely contact the surface of the rotating drum at this position because of the unevenness, and therefore, an image recorded on the printing plate by scanning with light beams may be out of focus or deformed, thereby exerting a bad influence upon image quality thereof.
In addition, if the nipping force of the holding member is weak, the printing plate does not closely contact the rotating drum and an image recorded thereon may be out of focus. This is due to firmness of the printing plate, and particularly is caused by the printing plate being shifted in a compressing direction at the edges thereof (nipping positions) in the peripheral direction of the rotating drum.
In view of the aforementioned, a primary object of the present invention is to provide a sheet member holding device which makes no scratch on a peripheral surface of a drum when holding the sheet member in close contact with the peripheral surface of the drum, holds edges of the sheet member with certainty, and prevents the sheet member from being partially lifted from the peripheral surface of the drum, thereby preventing deterioration of image quality.
In order to solve the above described problem, according to a first aspect of the present invention, there is provided a device for pressing and fixing a sheet member onto a rotating drum around which the sheet member is wound, the device comprising: (a) a support structure including a support which is mounted at a predetermined position on a peripheral surface of the drum; (b) a plate having two end portions, between which the plate is pivotably connected to the drum through the support structure; (c) a clamp element pivotably connected to one of the end portions of the plate, the sheet member being disposed between the clamp element and the peripheral surface; and (d) a resilient element connected to the other of the end portions of the plate, which resilient element is resiliently deformed when the support is mounted to the drum and, by applying a force to the other end portion of the plate, causes the one end portion of the plate to pivot toward the peripheral surface and press the clamp element against the sheet member, thereby resulting in a pressing force against the sheet member.
According to a second aspect of the present invention, there is provided a device for pressing and fixing a sheet member onto a rotating drum around which the sheet member is wound, the device comprising: (a) a support structure including a support which is mounted at a predetermined position on a peripheral surface of the drum; (b) a plate having two end portions, between which the plate is pivotably connected to the drum through the support structure; (c) a clamp element connected to one of the end portions of the plate so as to be translationally movable, the sheet member being disposed between the clamp element and the peripheral surface; and (d) a resilient element connected to the other of the end portions of the plate, which resilient element is resiliently deformed when the support is mounted to the drum and, by applying a force to the other end portion of the plate, causes the one end portion of the plate to pivot toward the peripheral surface and press the clamp element against the sheet member, thereby resulting in a pressing force against the sheet member.
According to a third aspect of the present invention, there is provided a device for pressing and fixing a sheet member onto a rotating drum around which the sheet member is wound, the device comprising: (a) a support structure including a support which is mounted at a predetermined position on a peripheral surface of the drum; (b) a plate having two end portions, between which the plate is pivotably connected to the drum through the support structure; (c) a clamp element attached to one of the end portions of the plate, the clamp element comprising a resiliently deformable portion, and the sheet member being disposed between the clamp element and the peripheral surface; and (d) a resilient element connected to the other of the end portions of the plate, which resilient element is resiliently deformed when the support is mounted to the drum and, by applying a force to the other end portion of the plate, causes the one end portion of the plate to pivot toward the peripheral surface and press the clamp element against the sheet member, thereby resulting in a pressing force against the sheet member.
According to a fourth aspect of the present invention, there is provided a device for pressing and fixing a sheet member onto a rotating drum around which the sheet member is wound, the device comprising: (a) a support structure including a support which is mounted at a predetermined position on a peripheral surface of the drum; (b) a first plate having two end portions, between which the first plate is pivotably connected to the drum through the support structure; (c) a second plate pivotably connected to one of the end portions of the first plate; (d) a clamp element attached to the second plate, the clamp element comprising a resiliently deformable portion, and the sheet member being disposed between the clamp element and the peripheral surface; and (e) a resilient element connected to the other of the end portions of the first plate, which resilient element is resiliently deformed when the support is mounted to the drum and, by applying a force to the other end portion of the first plate, causes the one end portion of the first plate to pivot toward the peripheral surface and press the clamp element against the sheet member, thereby resulting in a pressing force against the sheet member.
According to a fifth aspect of the present invention, there is provided a device for pressing and fixing a sheet member onto a rotating drum around which the sheet member is wound, the device comprising: (a) a support structure including a support which is mounted at a predetermined position on a peripheral surface of the drum; (b) a plate having two end portions, between which the plate is pivotably connected to the drum through the support structure; (c) a clamp element connected to one of the end portions of the plate so as to be translationally movable, the sheet member being disposed between the clamp element and the peripheral surface; (d) a resilient element connected to the other of the end portions of the plate, which resilient element is resiliently deformed when the support is mounted to the drum and, by applying a force to the other end portion of the plate, causes the one end portion of the plate to pivot toward the peripheral surface and press the clamp element against the sheet member, thereby resulting in a pressing force against the sheet member; and (e) a tensioning element provided at least at the other end portion of the plate, which, when the drum rotates, applies a pulling force to the clamp element via the plate due to centrifugal force.